Depends on which kit you have and the media. Some of the later kits had evergreen plastic rather than the wood construction.

Again (assuming wood), depending on the kit, I would either substitute plastic for wood, or take a MDC "Palace Car" and remove everything from the roof down and the ends in. Then replace wood with evergreen. The Westwood winds and doors are treasures.

I would be remiss if I didn't make the following observations:
These were some of the finest designed kits. Westwood also sold other parts to make more cars - a Solarium end, varying Observations ends, various windows and door parts, etc. Since the cars were of a modular construction, it was relatively easy to modify the cars to whatever configuration you wanted (within the obvious constraints). The obvious shortcoming was the vacuum formed roofs (built in sections) which is why I indicated the use of a MDC core.

The patterns for the windows, doors, and other detail parts were exquisite, and sorely missed today. Pullman's basic manufacturing technique was modular as well, and if someone with more money than (fiscal) brains were to create a line of parts and kits similar to the Westwood kits (which were for wood bodied cars) for classic HW cars, it would be a fantastic boon. Just a core for the 2xxx Plan cars would be especially welcome.

Basically, the same concept was used by New England Rail Service with their kits for modifying the Rivarossi "Pullman" into all sorts of configurations. The issue there was that the modeler had to saw/remove the side pieces to insert window and pillar sections. The Westwood model basically takes the side and you slide the windows and pillars onto a lower body.

I am trying to find the Sp Sunset Limited cars. We have 102, the parlor car. I got it on ebay. If you know of any of the SP kits for sale I would be interested. I also have several of the MDC palace car bodies that I could modify for the westwood parts.

I have found a few on eBay, but I have found far more at the Timonium railroad show. Not sure why the mid-Atlantic coast seems to have a lot of these kits floating around, but I can usually find at least one when I do go. Prices can be all over the board too.